The world's most expensive stamp, with a rich and colourful history, was displayed in London today ahead of its sale for more than £6 million later this month.

The only surviving 1856 one cent magenta from British Guiana has rarely been seen since it was last publicly exhibited in 1986.

On each of the three occasions it has been sold at auction, the stamp has set a new world record and it is expected to set yet another high when it goes under the hammer in New York on June 17.

The sliver of paper - which was shown off at the London base of Sotheby's today - is estimated to sell for between £6 million and £12 million.

It was found by a 12-year-old Scottish boy living in British Guiana, South America, who saw it as a nice addition to his stamp collection in 1873 when he found it among family papers, but had no idea that even at the time it was a rare find.

He sold it for a small sum later that year and within five years it was in the care of the renowned collector Count Philippe la Renotiere von Ferrary, an Austrian nobleman.

After he bequeathed it to a Berlin museum, it was seized by France in 1920 as part of First World War reparations from Germany and then sold on to a New York textile magnate.

It eventually ended up with John du Pont, heir to the chemical company fortune which bore his name, who bought it in 1980 for a then record price which would be equivalent to around £560,000.

The director of special projects at Sotheby's, David Redden, said of the stamp: " I have been with Sotheby's all my working life, but before I knew about the world's greatest works of art, before I knew about the Mona Lisa or Chartres Cathedral I knew about the British Guiana.

"For me, as a schoolboy stamp collector, it was a magical object, the very definition of rarity and value, unobtainable rarity and extraordinary value."